In order to support higher sensitivity of a solid-state imaging device and increase in the number of pixels in recent years, a photoelectric conversion layer stack type solid-state imaging device in which a photoelectric conversion portion including a pair of electrodes and a photoelectric conversion layer sandwiched between the pair of electrodes is provided above a silicon substrate so that electric charges generated in the photoelectric conversion layer are moved from one of the pair of electrodes to the silicon substrate and stored in the silicon substrate and a signal corresponding to the stored electric charges is read out by a signal reading circuit formed at the silicon substrate, has attracted much attention (see Patent Literature 1).
A configuration in which holes of the electric charges generated in the photoelectric conversion layer above the silicon substrate are stored in a charge storage portion in the silicon substrate and a signal corresponding to the holes stored in the charge storage portion is read out by the signal reading circuit in the photoelectric conversion layer stack type solid-state imaging device has been disclosed in Patent Literature 1. With such a configuration, sensitivity can be prevented from being lowered and spectral sensitivity can be prevented from being broadened even when an organic material is used for the photoelectric conversion layer.
In the solid-state imaging device according to Patent Literature 1, holes generated in the photoelectric conversion layer are stored in the charge storage portion made from a p-type impurity layer in the silicon substrate and a signal corresponding to the holes is read out by a p-channel MOS transistor. Alternatively, various systems are conceived as systems for reading out the signal corresponding to the holes. For example, there is conceived a configuration in which holes generated in the photoelectric conversion layer are stored in a charge storage portion made from an n-type impurity layer in the silicon substrate and a signal corresponding to the holes is read out by an n-channel MOS transistor.
However, in this configuration, there is a possibility that the potential of the charge storage portion will increase up to a voltage high enough to break down the n-channel MOS transistor or the like when excessive light is incident on the photoelectric conversion layer. In order to prevent the breakdown, a configuration in which a protection circuit is provided in the signal reading circuit has been described in Patent Literature 2.